370 



bark or alburnum of either the stem or the root, he proceeded to in- 

 vestigate the states of the leaf, and of the succulent annual shoot. 

 With this view various grafts of the golden pippin, which were known 

 to be liable to decay, were inoculated with buds of new varieties ; 

 and in the ensuing winter their own natural buds were removed, and 

 those that had been inserted were alone allowed to remain. As soon 

 as the leaves of these began to appear, every symptom of disease was 

 removed ; and each part of the branch of the golden pippin thus re- 

 generated, appeared to perform its office as well as the wood and 

 bark of the seedling stock could have done without this intermediate 

 graft of old materials. 



Since the vigour of youth, or debility and diseases of old age, ap- 

 peared thus to depend on the quality of the leaf through which the 

 sap of plants circulates, in the same manner as the blood of animals 

 does through their lungs, Mr. Knight considers the consequence of 

 defective leaves, according to his former views of the functions they 

 perform, of preparing and assimilating the sap transmitted through 

 them ; and he observes, that the deficiency of power in the leaves is 

 (as might be expected) most apparent where the redundancy of sap 

 is the greatest ; for he finds that the grafts of old varieties are most 

 diseased in rich soils, or when they are applied to vigorous stocks ; 

 and the defects appear to arise from an accumulation of fluid in the 

 extreme branches and annual shoots, beyond what can circulate with 

 effect through the imperfect leaves that are produced by extremities 

 debilitated by age. 



In support of this opinion, of an essential difference between the 

 leaves of young and of old varieties, Mr. Knight observes, that there 

 is an evident alteration in the character of leaves visible in the same 

 variety, between those of two years and those of twenty years old ; 

 and that it is consequently highly probable that still further changes 

 have occurred in the course of two centuries. 



From these results respecting the importance of the leaves to the 

 well-being of vegetables, the author ventures to suggest the proba- 

 bility, that the debilities of old age in animals may arise from a si- 

 milar source, and may be traced to injury primarily sustained by the 

 lungs. 



It is not merely upon general analogy that such an opinion may 

 be supported, but in particular instances of long life in men and in 

 domesticated animals, it is observed that those individuals longest 

 retain their health, and are most able to bear excessive labour with- 

 out injury to their constitution, in whom the chest is manifestly most 

 capacious. 



On the Gizzards of Grazing Birds. By Everard Home, Esq. F.R.S. 

 Read April 4, 1810. [Phil. Trans. 1810, p. 184.] 



Since the organs of digestion in those quadrupeds which live 

 wholly upon grass differ considerably in their construction from those 



